MAGNETISM Basic Electrical TheoryExample: Calculate the ampere-turns for a coil with 1000 turns and a 5 mA current.N = 1000 turns and I = 5 mAsubstituteN = 1000 turns and I = 5 x 10-3NI = 1000 (5 x 10-3) = 5 AtFieldIntensityWhen a coil with a certain number of ampere-turns is stretched to twice its length, the magneticfield intensity, or the concentration of its magnetic lines of force, will be half as great. Therefore,field intensity depends on the length of the coil. Equation (1-14) is the mathematicalrepresentation for field intensity, which is related to magnetomotive force as shown.(1-14)HFMLNILwhereH = field intensity,AtmNI = ampere-turns (At)L = length between poles of coil (m)FM= Magnetomotive force (mmf)Example 1: Find field intensity of an 80 turn, 20 cm coil, with 6A of current.Solution:N = 80, I = 6A, and NI = 480 AtH480 At0.2 m2400 AtmExample 2: If the same coil in Example 1 were to be stretched to 40 cm with wire length andcurrent remaining the same, find the new value of field intensity.Solution:N = 80, I = 6A, and NI = 480 AtH480 At0.4 m1200 AtmES-01 Page 34 Rev. 0